Frames for bicycles, motorcycles, and the like are often formed by joining together sections of at least partially hollow tubing (regardless whether the tubing has a round or annular cross-section, rectangular cross-section, or cross-sections having one or more other geometries). The joints where such tubing sections intersect often include internal openings leading from one tube to another tube, which may form a passageway for water, oil or other types of moisture, dust, salt, sand, or other types of debris to migrate within the frame tubing. This can lead to unwanted, undetected, and potentially dangerous internal corrosion of the frame tubes and other components housed within the frame, such as bearings. In the case of electric bicycles that house electronic components at least partially within the tubing of the frame, the presence of moisture or other unwanted substances within the tubing of the frame can lead to failure of electronic components. Access points where liquid or solid substances from the outside environment can sometimes enter inside the tubing of a frame may include tubes that are open on at least one end, such as seat post tubes, swingarm tubes, crankshaft bottom brackets, and head tubes, for example.
Some efforts have been made to seal the tops of bicycle frame head tubes, for instance, from the outside environment. See for instance U.S. Pat. No. 7,441,961 B2 issued to Li on Oct. 28, 2008 (“Li”), which is incorporated herein by reference. But these efforts have been primarily directed to providing some (typically imperfect) protection for bearings housed within the tubes, and not to dealing with liquid or solid substances that enter the hollow frame tubes or to preventing migration of such materials within the tubes. A need remains for a feasible and robust way to prevent or impede liquid or solid substances from entering and migrating within the hollow tubes of a frame.